The Paris prosecutor's office said late on July 21 that it has filed terrorism charges against five accomplices of the truck driver who killed 84 people on a beachfront in Nice, France.

Prosecutors said the driver, Mohamed Lahouaiej Bouhlel, who was shot dead at the scene on July 14, and his accomplices appeared to have been plotting the attack for months. They cited text messages, more than 1,000 phone calls, and video of the attack scene on the phone of one of the suspects.

Prosecutor Francois Molins' office, which oversees terrorism investigations, has put more than 400 investigators on the case and is pursuing a battery of charges against the five suspects, including complicity to murder and possessing weapons tied to a terrorist enterprise.

The detained suspects are four men -- identified as Franco-Tunisians Ramzi A. and Mohamed Oualid G., a Tunisian named Chokri C., and an Albanian named Artan -- and a woman of dual French-Albanian nationality identified as Enkeldja.

Ramzi had previous convictions for drugs and petty crime. All were imprisoned pending further investigation.

People close to Bouhlel, a French-Tunisian who had lived in France legally for years, said he had shown no signs of radicalization until very recently. But prosecutors said information from Bouhlel's phone suggested he could have been preparing an attack as far back as May 2015.

Evidence suggests Bouhlel staked out the Bastille Day fireworks event in Nice in 2015 as he prepared for the attack, in which he used a 19-ton truck to mow down 84 people who were leaving the 2016 Bastille Day fireworks show, Molins said.

The Islamic State group has claimed responsibility for the attack. Authorities say they have no found signs the extremist group actually directed or funded it, although their evidence confirms the attack was premeditated.

Prosecutors used telephone records and social-media posts to link the five suspects to Bouhlel and the attack.

On April 4, Tunisian Chokri C. sent Bouhlel a Facebook message reading: "Load the truck with 2,000 tons of iron... release the brakes my friend and I will watch."

Video surveillance placed Chokri with Bouhlel in the truck on Nice's Promenade Des Anglais before Bouhlel set off on his murderous rampage, driving the truck more than a mile along the famous waterfront avenue as it was crowded with people.

Chokri's fingerprints have been found on one of the truck doors. Pictures of Oualid apparently taken in the truck used in the attack were also found on Bouhlel's phone.

Hours after the attack, prosecutors said one of the accomplices also filmed the bloody scene on the promenade.